Plastic anisotropy evolution of SS316L and modeling for novel cruciform specimen

In this paper, the evolution of the plastic anisotropy of stainless steel 316L samples is investigated under proportional loading paths using a customized cruciform specimen. The determination of a novel cruciform specimen by a design of experiments approach integrated with finite element simulations is described. The mechanical properties of the material are characterized under uniaxial tension applied in every 15° from the rolling direction and equibiaxial tension from hydraulic bulge experiments. The results reveal that the plastic anisotropy shown in stress and strain significantly evolves with respect to the plastic work. Based on the experiments, the material behavior is modeled using a non-quadratic anisotropic yield function, Yld2004–18p, with parameters modeled as a function of the equivalent plastic strain, assuming plastic work equivalence, and with constant parameters for comparison. The Hockett-Sherby model is also used for the strain hardening behavior to extrapolate the results to higher strain values. The models are implemented into a user material subroutine for finite element simulations. To validate the model, in-plane biaxial tension experiments are performed, using a customized specimen, to achieve greater deformation than previous designs by introducing double-sided pockets for thickness reduction and notches in the corner areas. The results are compared with finite element simulations implemented with the plasticity models

DIC Challenge: Developing Images and Guidelines for Evaluating Accuracy and Resolution of 2D Analyses

With the rapid spread in use of Digital Image Correlation (DIC) globally, it is important there be some standard methods of verifying and validating DIC codes. To this end, the DIC Challenge board was formed and is maintained under the auspices of the Society for Experimental Mechanics (SEM) and the international DIC society (iDICs). The goal of the DIC Board and the 2D-DIC Challenge is to supply a set of well-vetted sample images and a set of analysis guidelines for standardized reporting of 2D-DIC results from these sample images, as well as for comparing the inherent accuracy of different approaches and for providing users with a means of assessing their proper implementation. This document will outline the goals of the challenge, describe the image sets that are available, and give a comparison between 12 commercial and academic 2D-DIC codes using two of the challenge image sets.status: publishe

An autonomous design algorithm to experimentally realize three-dimensionally isotropic auxetic network structures without compromising density

Auxetic materials have a negative Poisson’s ratio and are of significant interest in applications that include impact mitigation, membrane separations and biomedical engineering. While there are numerous examples of structured materials that exhibit auxetic behavior, the examples of engineered auxetic structures is largely limited to periodic lattice structures that are limited to directional or anisotropic auxetic response. Structures that exhibit a three-dimensionally isotropic auxetic response have been, unfortunately, slow to evolve. Here we introduce an inverse design algorithm based on global node optimization to design three-dimensional auxetic metamaterial structures from disordered networks. After specifying the target Poisson’s ratio for a structure, an inverse design algorithm is used to adjust the positions of all nodes in a disordered network structure until the desired mechanical response is achieved. The proposed algorithm allows independent control of shear and bulk moduli, while preserving the density and connectivity of the networks. When the angle bending stiffness in the network is kept low, it is possible to realize optimized structures with a Poisson’s ratios as low as −0.6. During the optimization, the bulk modulus of these networks decreases by almost two orders of magnitude, but the shear modulus remains largely unaltered. The materials designed in this manner are fabricated by dual-material 3D-printing, and are found to exhibit the mechanical responses that were originally encoded in the computational design engine. The approach proposed here provides a materials-by-design platform that could be extended for engineering of optical, acoustic, and electrical properties, beyond the design of auxetic metamaterials